1. Field of the invention
The invention relates to a tissue transmitted light sensor which detects a change of the quantity of transmitted light due to absorptive substances in the blood flowing through an arterial vascular of the subject, thereby detecting the pulse wave of the blood, and particularly to a tissue transmitted light sensor which detects the pulse wave on the basis of light transmitted through a tissue in the vicinity of the superficial temporal artery.
2. Related art
In order to measure the oxygen saturation of the blood of the subject or the cardiac output, the blood volume, etc. with injecting dye in the blood, pulse photometry is used. A known probe for the pulse photometry, is an optical sensor probe which is to be attached on an earlobe, an ear concha, a fingertip, or the like. In the probe, a light emitting unit such as an LED emits light and a light receiving unit such as a photo diode PD receives the light, thereby detecting absorptive substances in the blood flowing through an arterial vascular in the tissue in the vicinity of the attached part.
The conventional optical sensor probe configured as described above has a problem in that, in the case where the probe is attached on a fingertip, the flow rate of the blood is varied when vasomotor nerves are irritated by reflex due to hyper ventilation or an injection so that a measure value becomes unstable.
In the case where the probe is attached on an ear, a measure value is hardly affected by vasoconstriction due to reflex. In this case, however, there arises a problem in that the amplitude of the pulse wave is much lower than that in a fingertip and, particularly for a patient under general anesthesia or immediately after operation, the measurement cannot be stably conducted.
When the cardiac output, the blood volume, etc. are to be measured by using dye, the attachment of the probe may cause a blood flow impediment. This produces a problem in that the measurement accuracy and reproducibility are impaired. Furthermore, the clip method which is often used for attaching a probe to an earlobe has a defect that, when the subject moves, the probe easily swings and hence it is difficult to conduct the measurement stably and highly accurately, thereby easily producing a measurement error.